The Volucella, that sanitary inspector of the Vespian city, fulfils a double office: she gives the Wasp’s children a wipe down; and [[306]]she rids the Wasps’-nest of its dead. For this reason, she is peacefully received, as an assistant, when she enters the burrow to lay her eggs there; for this reason, her grub is tolerated, nay more, respected, in the very heart of the dwelling, where none might stray with impunity. I remember the brutal welcome accorded to the Saperda- and Hylotoma-larvæ when I place them upon a comb. Forthwith grabbed, bruised and riddled with stings, the poor wretches perish. It is quite a different matter with the offspring of the Volucella. They come and go as they please, poke about in the cells, elbow the inhabitants and remain unmolested. Let us give some instances of this clemency, which is very strange in the irascible Wasp.
For a couple of hours, I fix my attention on a Volucella-grub established in a cell, side by side with the Wasp-grub, the mistress of the house. The hind-quarters emerge, displaying their papillæ. Sometimes also the pointed fore-part, the head, appears, bending from side to side with sudden, Snake-like motions. The Wasps have just filled their crops at the honey-puddle; they are dispensing the rations, are very busily at work; and these things are taking place in broad daylight, on my table, by the window. [[307]]
As they pass from cell to cell, the nurses repeatedly brush against and stride across the Volucella-grub. There is no doubt that they see it. The intruder does not budge, or, if trodden on, retires inside, only to reappear the next moment. Some of the Wasps stop, bend their heads over the opening, seem to be making enquiries and then go off, without troubling further about the state of things. One of them does something even more remarkable: she tries to give a mouthful to the lawful occupant of the cell; but the larva, which is being squeezed by its visitor, has no appetite and refuses. Without the least sign of anxiety on behalf of the nurseling which she has seen in awkward company, the Wasp retires and goes to distribute her ration elsewhere.
In vain I prolong my examination: there is no fluster of any kind. The Volucella-grub is treated as a friend, or at least as a visitor that does not matter. There is no attempt to dislodge it, to worry it, to put it to flight. Nor does the grub seem to trouble greatly about those who come and go. Its tranquillity tells us that it feels at home.
Here is some further evidence: the grub has plunged, head downwards, into an empty cell, which is too small to contain the whole [[308]]of it. Its hind-quarters stick out, very visibly. For long hours it remains motionless in this position. At every moment Wasps pass and repass close by. Three of them, at one time together, at another separately, come and nibble at the edges of the cell; they break off particles which they reduce to paste for a new piece of work.
The passers-by, intent upon their business, may not perceive the intruder; but these three certainly do. During their work of demolition, they touch the grub with their legs, their antennæ, their palpi; and yet none of them minds it. The fat grub, so easily recognized by its queer figure, is left alone; and this in broad daylight, where everybody can see it. What must it be when the profound darkness of the burrows protects the visitor with its mysteries!
I have been experimenting all along with big Volucella-grubs, coloured with the dirty red that comes with age. What effect will pure white produce? I sprinkle on the surface of the combs some larvæ that have lately left the egg. The tiny, snow-white grubs make for the nearest cells, go down into them, come out again and hunt about elsewhere. The Wasps peaceably let them go their way, as heedless of the little white [[309]]invaders as of the big red ones. Sometimes, when it enters an occupied cell, the little creature is seized by the owner, the Wasp-grub, which nabs it and turns it over and over in its mandibles. Is this a defensive bite? No, the Wasp-grub has merely blundered, taking its visitor for a proffered mouthful. There is no great harm done. Thanks to its litheness, the little grub escapes intact from the grip and continues its investigations.
It might occur to us to attribute this tolerance to some lack of penetration in the Wasps’ vision. What follows will undeceive us: I place separately, in empty cells, a larva of the Scalary Saperda and a Volucella-larva, both of them white and selected so as not to fill the cell entirely. Their presence is revealed only by the paleness of the hind-part, which serves as a plug to the opening. A superficial examination would leave the nature of the recluse undecided. The Wasps make no mistake: they extirpate the Saperda-grub, kill it, throw it into the rubbish-pit; they leave the Volucella-grub in peace.
The two strangers are quite well recognized in the secrecy of the cells: one is the intruder that must be turned out; the other [[310]]is the regular visitor that must be respected. Sight helps, for things take place in the daylight, under my cage; but the Wasps have other means of information in the dimness of the burrow. When I produce darkness by covering the apparatus with a screen, the murder of the trespassers is accomplished just the same. For so say the police-regulations of the Wasps’-nest: any stranger discovered must be slain and thrown on the midden.
To thwart this vigilance, the real enemies need to be masters of the art of stealthy immobility and cunning dissimulation. But there is no dissimulation about the Volucella-grub. It comes and goes, openly, wheresoever it will; it looks round amongst the Wasps for cells to suit it. What has it to make itself thus respected? Strength? Certainly not. It is a harmless creature, which the Wasp could rip open with a blow of her shears, while a touch of the sting would mean lightning death. It is a familiar guest, to whom no denizen of a Wasp’-nest bears ill-will. Why? Because it renders good service: so far from working mischief, it does the scavenging. Were it an enemy or merely an intruder, it would be exterminated; as a deserving assistant it is respected. [[311]]